The objective of the proposed research is to construct a prototype narrow- bandwidth x-ray source for medical imaging using a new, efficient hybrid radiator driven by a relativistic electron beam of moderate energy and current. The high x-ray yield (photons/electron) of the source permits the use of modest electron-beam currents preventing thermal damage to the radiator itself. Since the source is inherently collimated and quasi- monochromatic it will produce higher quality radiographic images while lowering the dose to the patient. A preliminary experiment has demonstrated intense quasi-monochromatic x-rays in the range optimum for mammography. A preliminary calculation of the x-ray yield will be expanded to include various parameter ranges where different x-ray generation mechanisms dominate. The research will proceed by optimizing the design of the hybrid radiator and experimentally demonstrate its feasibility by use of a compact betatroN wherein the electrons are recycled through the radiator many times. The later will increase the overall system efficiency many times. The potential for successful development of the prototype imaging system is very high because our preliminary experiment has demonstrated efficient narrow-bandwidth x-ray generation in the region optimal for mammography. We will show that these results indicate that a high quality mammogram can be generated in less than 3 seconds. PROPOSED COMMERCIAL APPLICATIONS: An efficient x-ray source with characteristics similar to the synchrotron has benefits of making high x-ray fluxes more accessible without radiator damage. This work is directly applicable to mammography since the directional-, quasi-monochromatic-source permits reduced scattering while the narrow bandwidth and frequency selection optimizes contrast and reduces dose.